Preparation of 2,6-diaminoanthraquinone/reduced graphene oxide-based composites as cathode materials for organic lithium batteries

Organic carbonyl compounds have received great attention as electrode materials because of their fast reduction–oxidation kinetics, environment friendliness, and high theoretical capacity. Especially, the small molecular quinones, such as anthraquinone (AQ), can possess high theoretical (257 mA·h·g⁻¹) and a discharge–charge voltage of 2.2–2.3 V, implying that it has the potential of up to 565 W·h·kg⁻¹ energy density. However, it suffers from high solubility in organic electrolytes and low conductivity, leading to rapid capacity fading and inferior rate performance. Herein, we report 2,6-diaminoanthraquinone (2,6-AAQ) uniform self-assembly into a three-dimensional (3D) porous structure graphene foam, which was successfully fabricated through a gentle hydrothermal synthesis reaction with simultaneous in situ condensation of 2,6-AAQ on the reduced graphene surface, as a high-performance cathode for Lithium-organic batteries. Benefiting from the formation of a covalent bond (—CO—NH—) between the amino group (—NH₂) of 2,6-AAQ and the carboxyl group (—COOH) of oxidized graphene, the molecular structure of AQ is uniformly anchored into a 3D graphene foam architecture. The strategy simultaneously solved the high dissolution and low conductivity of AQ. The as-obtained hybrid composites were characterized by various techniques. SEM and EDS mapping images demonstrated that the 2,6-AAQ within the hybrid architecture was not only uniformly anchored on the surface but also tightly wrapped in the interior of graphene foam. This unique architectural structure can improve the electronic conductivity of 2,6-AAQ in the lithiation process and effectively inhibit the dissolution of 2,6-AAQ in electrolytes, which is beneficial to hoist the electrochemical performance of the composite materials. XPS, XRD, FTIR, and Raman results indicated that hydrothermally assisted chemical bonding occurred between 2,6-AAQ and rGO, significantly facilitating the mass electron transformation and ion diffusion from graphene substrate to 2,6-AAQ for the fast reduction–oxidation reaction. Combined with the above results, UV–Vis spectroscopy tests also further disclosed that the 2,6-AAQ and rGO linked by covalent bonds significantly decrease solubility compared with 2,6-AAQ, indicating the greatly increased cycling stability of the hybrid material. Additionally, ex situ FTIR characterization results verified that the composite cathode material with two carbonyls (C=O) active sites has good lithium storage performance. By optimizing the 2,6-AAQ concentration, the 25% 2,6-AAQ in the as-prepared composite was used as the high-performance cathode for the lithium-ion battery. The composite material can display a high initial discharge capacity of 212.2 mA·h·g⁻¹ at 100 mA·g⁻¹ (based on the 2,6-AAQ mass) and a reversible capacity of 184 mA·h·g⁻¹ with a capacity retention of 86.7% after 100 cycles at 500 mA·g⁻¹ current density. This excellent electrochemical performance is attributed to fast lithium-ion diffusion and electric transport between the 2,6-AAQ and the 3D porous structure hybrid architecture, which also proposes a facile strategy for the immobilization of the small molecular quinones to construct advanced organic lithium batteries.